Pressure Sensor Calibration via Repeated Location Visits
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Solution Overview
Problem
Smartphones and other mobile devices rely on unstable sensors like pressure sensors and accelerometers, which suffer from drift over time, leading to erroneous measurements and inaccurate positioning, particularly in critical applications such as emergency response.
Innovation Solution
A method is developed to calibrate these unstable sensors by determining calibration values through repeated visits to known locations, using relative and absolute calibration adjustments to correct pressure measurements, thereby improving the accuracy of altitude estimation and reducing errors caused by sensor drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low cost pressure sensors are used in mobile devices, then device cost is reduced, but measurement precision deteriorates due to sensor drift over time
Solution Approach 1:
The system uses GPS location feedback to identify when the mobile device returns to a known location, retrieves previously stored calibration data, and applies correction factors to compensate for sensor drift. This closed-loop feedback mechanism maintains measurement precision without requiring expensive stable sensors.
Solution Approach 2:
The system performs preliminary calibration at known locations before drift occurs, storing calibration data for later use. By pre-establishing reference measurements at documented locations, the system can correct future measurements without real-time intervention.
2Measurement precision
If pressure sensors are calibrated at manufacture or installation, then initial measurement precision is improved, but reliability deteriorates over time due to drift in field conditions
Solution Approach 1:
The system continuously recalibrates the pressure sensor by repeatedly visiting known locations and updating calibration data. This continuous calibration process maintains reliability over time by constantly correcting drift rather than relying on a single initial calibration.
Solution Approach 2:
The system performs self-calibration by automatically detecting when it returns to known locations using GPS, retrieving appropriate calibration data, and applying corrections without user intervention. The mobile device calibrates itself using its own movement patterns and stored location data.
3Measurement precision
If calibration values are determined through repeated visits to known locations, then measurement precision is improved, but loss of time increases due to multiple visits required
Solution Approach 1:
The system performs calibration data collection during normal device usage by automatically detecting visits to known locations. Rather than dedicating separate calibration sessions, the system continuously gathers calibration data whenever the device naturally returns to documented locations, making the calibration process ongoing and integrated with normal use.
4Measurement precision
If sensor drift is corrected using relative and absolute calibration adjustments, then measurement precision is improved, but device complexity increases due to multiple calibration values
Solution Approach 1:
The system extracts the calibration management complexity from the pressure sensor itself and places it in the software layer. By separating the simple pressure sensing function from the complex calibration logic, the system maintains measurement precision while keeping the core sensor simple and the calibration processes manageable through software algorithms.
Data Source
AI summary
Calibrating a pressure sensor of a mobile device includes determining a first plurality of calibration values for a first plurality of visits to a first revisit zone to which a mobile device repeatedly returns; determining a first relative calibration adjustment value based on the first plurality of calibration values; determining an adjusted absolute calibration value based on i) an absolute calibration value used to calibrate pressure measurements made by a pressure sensor of the mobile device, and ii) the first relative calibration adjustment value; and calibrating pressure measurements made by the pressure sensor of the mobile device using the adjusted absolute calibration value.